This invention relates to a method and apparatus for automatically inspecting and repairing an active matrix LCD panel. Inspection is achieved by electro-optic voltage imaging, while repair is achieved by laser cutting and material deposition. The inspection process results in the performance information and the generation of a list of panel defects, including the type and location of each defect. Automated repair is performed by accessing such list to identify a defect to be repaired. Prescribed repair operations are performed based upon the defect type and location.
Conventional display panel manufacturing yields have been unsatisfactory, causing display panel cost to be a large portion of the final cost of a micro-computer system. In addition, testing of display panels has been difficult. For active matrix LCD panels the problem is even more troublesome. Active matrix LCD panels have added complexity over the prior simple matrix panels. In addition to the need for satisfactory continuity among electrode lines and adequate resistance levels, active matrix panels have multilayer insulation and dynamic switching characteristics. The precise location of the defect is important information about the panel fabrication process.
Circuit panels such as active matrix LCD panels include a plurality of connections and independent circuits on a flat surface. Because the densities available for such panels are increasingly high and the spacing between circuit lines are decreasingly small, defects frequently occur during the manufacturing and assembly processes. For high density active matrix LCD panels, a typical yield of shipped panels is approximately 10%. Such panels require an array of thin-film transistors to be fabricated on a large glass substrate (e.g., active plate). The number of thin-film transistors often surpasses one million, while the process area can be as large as 350 cm.sup.2. Such volumes and densities present a formidable yield challenge even for VLSI and ULSI manufacturing processes. Because of the significant percentage of defective panels, 100% testing of each such panel is common.
Active matrix LCD panels are formed by an active plate as described above, along with polarizers, filters, sealant and additional materials. Any defects which occur in the active plate conventionally go undetected until final assembly. Conventionally, such panels are activated and visibly inspected for pixels which do not activate. Once the panel is fully assembled, sealed and filled, the components typically cannot be reworked and reused.
Accordingly, there is a need for an automatic system for identifying defects early in the manufacturing process (e.g., in-process inspection) so as to avoid subsequent manufacturing steps for panels having a large number of defects. Further, there is a need for a method and apparatus for repairing panels having sufficiently few defects. In addition, there is a need for automating and linking the inspection and repair processes so as to increase test throughput.